The present invention relates to a pulp making technology using herbaceous plants, more particularly, to a method for making pulp from cornstalk.
Using cornstalk as a raw material for pulp making can replace import of raw wood material, so that it can save foreign currency, increase rural income and make high-quality paper.
At present, Korea, with increasing national income, is a tenth manufacturing country in the world (paper and board production of 5,830,000 tons/year) as well as a seventh paper consuming country, in publications, newspapers, boards for publishing, graft papers and bulk papers. Total amount of pulp to prepare papers, however, entirely (100%) depends on foreign markets. Because developing pulp industries will impair forest resources, new pulp materials should be developed. To do so, we should manufacture and process cellulose materials from various plant species and improve their utility value. Species of trees in Korea are not proper for pulp making, domestic wood production for pulp preparing is not enough, and thus raw materials for pulp making can't be secured. Therefore studies to find new turning point in terms of pulp making are frequently reported.
Conventionally, pulp for paper-making is mostly from wood. However, as recently worldwide shortage of wood resources is deepened, it has become a big issue to manufacture pulp and paper without destroying forests and environment. As a plan to solve this problem, technologies of pulp making from non-wood plant fibers, using one or two years plants as main materials, have been taken notice. To ensure providing materials for pulp making, in China, Middle Ease and India, which face the shortage of forests resources, national-widely tend to concentrate on developing pulp material using herbs such as bamboos and farm wastes, and developing pulp manufacturing processes using wastes of sugar canestalks abolished after sugar production.
Generally, non-wood plants tend to contain lots of pectin, hemi-celluloses and inorganic substances, but a little bit of lignin. In order to make pulp from non-wood plant, chemical, semi-chemical or mechanical methods are used, and unbleached or bleached pulp can be obtained under very mild conditions compared with wood materials. Each non-wood pulp has different characteristics according to its fiber form, chemical composition, and types and amount of non-fiber cells. Therefore, papers manufactured from non-wood pulp alone or appropriately combined with wood pulps have used in more various usages according to strength, permanence, electrical characteristics, luster, dimension stability and feature of publishing performance, and their utilizations have been extended.
Paper mulberry inner bark, flax, hemp, cotton plant, Manila hemp, and etc. are examples of non-wood plants. There have previously been attempts in the art to provide pulp manufacturing methods using bagasses (as disclosed in Korean Patent Laid-open No. 84-005762), dry pine needles gathered from fallen leaves (in Korean Patent Laid-open No. 91-3216), or rice stalks (in Korean Patent Laid-open Nos. 98-9651 and 93-2604), as law materials for pulp making. In addition, Korean Patent Application No. 85-5895 discloses a method for preparing pulp from cigarette stalks.
To the inventor's knowledge, a method for preparing pulp from cornstalks has not been recognized in any document, nor mentioned in any report to date.
Corn cultivated in rural district is used for food or livestock feed. Most cornstalks are crushed and scattered to fertilize the soil, although some of those are used as a livestock. It is seriously required to find the alternative raw materials for preparing pulp, so as to minimize unnecessary foreign currency waste, and need to use farm wastes usefully to increase rural income. There is also a need of developing high-quality paper. Therefore, it is necessary to process cornstalks in novel way and raise their utility value in making pulp or other pulp-like materials.
Now, the present invention made an attempt to prepare a novel and peculiar pulp from cornstalks and manufacture the paper having high-quality and unique characteristics. At present, because paper making and dissolving pulp is prepared by separating fibrous cellulose from wood sources in most of countries, more than 90% of pulp production in the world are wood pulps.
Koreans have been long produced Korean paper from paper mulberry barks, as a Korean pure specialty having peculiar characteristics distinct from western paper in terms of physical properties. Korean paper is much superior in terms of durability, heat insulation and air permeability. In conventional Korean paper preparation, paper mulberry barks are collected in every October and November, boiled in a kettle, and debarked to leave white inner bark alone. The outer barks are boiled well in the buckwheat lye and mashed by beating with a wooden hammer so as to be softened. Then, the obtained paper mulberry juice is added into a paper peeling tank to obtain paper sheets.
In the manufacture of a wood-based cellulose pulp, it is necessary to develop a selective reagent reactive not to celluloses but to lignin under exposure to the timber. Since the pulp making process is a combination of wastewater recovery and waste treatment processes in terms of environment conservancy, the wood pulp manufacturing industry is considered as a capital-intensive large-scaled equipment and an energy-intensive industry using a large amount of water.
The chemical pulp preparation is composed of a pulping step for removing lignin among wood ingredients, and a pulp bleaching and purifying step for selectively eliminating residual impurities in pulp. The chemical pulp preparation method considerably varies depending on the usage and required quality of the final pulp product. The conventional pulp used for paper manufacturing is made from softwood and hardwood. Such raw materials are processed into wood pulp by mechanical, chemical and semi-chemical methods. The mechanical pulping process consists of debarking, cutting, grinding, coarse screening, fine screening, centrifugal cleaning, thickening, bleaching, washing, drying and packing. Meanwhile, the chemical pulping process consists of debarking, chipping, cooking, coarse screening, fine screening, washing, centrifugal cleaning, thickening, bleaching, drying and packing.
Specifically, there are two types of pulp, paper-making pulp and dissolving pulp. The dissolving pulp is prepared by the pre-treatment and chemical pulping to get high purity cellulose product and used for the manufacture of various cellulose polymer products and preparation of cellulose derivatives having high alpha-cellulose content of 90–98%. Semi-chemical pulping process consists of mild chemical treatment and mechanical defibering process to separate pulp fiber.
In a kraft method, for removing lignin from timber, nucleophilic groups such as —OH, —SH and —S2 in alkaline cooking liquor attack the lignin polymer constituted by phenylpropane units to produce phenol hydroxyl groups, quinonmethide formed thereby reacts with the neucleophilic reagent to generate a sulfurization reaction, and then the lignin polymer is degraded to be dissolved in the alkaline solution. In an acidic sulfite method, phenolic ether bonds are hydrolyzed by H+ to produce, bisulfite ions bind to carbonium ions, and the lignin polymer is converted to water-soluble lignosulfate. However, in the methods using a cooking reagent selectively reactive to lignin polymer rather than other polymer ingredients of the wood, cooking liquor is a strong alkaline or acid solution. Also, high-purity fibrous celluloses cannot be separated by those methods, because parts of the celluloses are decomposed at high temperature controlled in the range of about 150–170° C. to achieve an economical lignin separation rate. Accordingly, considering pulp yield and economical aspects, the paper making pulp must be subjected to a bleaching step to obtain high level of brightness through a selective removal method for residual lignin comprising at least five-stage oxidation and/or reduction, and alkaline extraction.